Power tube rolling in the Archon 50


Really knows where his towel is.
Sep 16, 2013
Dublin, OH
My Archon 50 head came stock with a pair of JJ 6L6s. but the amp will also take EL34s and KT66s. I've been wanting to try those out, especially KT66s. So, through the magic of Amazon, I came into a pair of JJ E34Ls and a pair of Shuguang KT66s and tried them out in the Archon. Also, just for grins, I decided to do a test shot with my JJ 6V6Ses, just to see if they would tolerate the voltages.

JJ 6L6s: These started out biased super cold in my amp for some reason. Like, biased by Peavey cold. OTOH, biasing them in the PRS recommended range (~30mA) didn't really change the sound much. These are the standard tubes for the Archon, and they sound pretty good.

JJ 6V6s: These worked without too much trouble, surprisingly. I biased them to ~20mA based on some assumptions/guesses about the amp's B+ voltage range and the JJ 6V6's plate dissipation rating. (I would not want to try EHX or other current production 6V6s in this amp!) Anyway, they sounded OK but nothing special -- as you might expect, they put out less bass and a little less volume than the 6L6s. If this is how the MT15 sounded with 6V6s, I understand why they went with 6L6s instead.

JJ E34Ls: I was surprised that these biased (~30mA) and sounded almost exactly like the JJ 6L6s. I expected to hear a bit of bass cut and mid boost, but other than the slightly bigger bottles and hotter heaters, they're pretty much indistinguishable from the 6L6s. Maybe I'm just not playing loud enough to hear a difference.

Shuguang KT66s: Wow. These are huge compared to the 6L6s and E34Ls -- they just barely fit in the amp, and they biased (~40mA) and run super hot compared to the others. They sound huge as well, with deeper bass and treble and a little more mids than the 6L6s. The Archon already has a pretty wide frequency spectrum, and IMHO the KT66s make it even wider.

After the experiments, the KT66s went back in for the foreseeable future. They sound freaking awesome.
That parallels my experience with most of those same tubes in a THD Flexi some time ago. The JJ 6V6s are pretty tough, and I enjoyed torturing them in the Flexi for a while. I could run 'em harder than higher-output tubes which shaved maybe a few dB off the SPL's when played in anger.
Your 6L6 vs EL34 comparison confirms what I experienced going from one to the other in a Mesa I had a few years ago. There were subtle differences; the amp got a titch tighter; that was about it.

Maybe ten years ago, I had a Bad Cat Hot Cat 30 with EL34s. If anything, the amp sounded very much like the EL84 Matchless/Hot Cat/Vox-ish amps, but with a bit more punch, and a more piano-like low end.

I’ve played some really nice sounding KT66 amps lately, one of which is the 100 Watt Metropoulos Superplex, a very impressive mid-late 60s-sounding lower gain amp. And yeah, those tubes seem to have a big, rich tone.
I’ve always assumed I was an EL34 guy, loving Marshalls the way I do. And, I’ve loved the Archon so much that I haven’t yet even tried them in it. But what I’m hearing is that I should probably get some KT66 before I try EL34 or EL34B.
I had one of the first generation 3-channel dual rectos, that I spent lots of time experimenting with tubes. I came to a lot of the same conclusions. Basically 6L6’s have a slight upper mid scoop, EL34’s a slight low mid scoop, and KT66’s no scoop. KT66’s ended up being my main choice. But I never stopped swapping them out haha. I even had a bunch of preamp tubes I experimented with, including an old ge 5751 that was killer as a first gain stage.

Then I read a trick about turning the treble knob all the way down. That was my favorite trick of all. Suddenly the amp gets its punch back. Like there’s a compressor that gets turned off. Anyway due to changes in life, I didn’t need a 100 watt beast anymore and sold it. Eventually bought a stiletto ace. Then sold it. Bought and sold several others, but rarely use a real amp these days. But that stiletto is the amp I want back more than any I’ve had.

One of these days I’ll try some of the prs amps. The new mt15 looks killer, but from what I’ve seen, I’d never get the gain knob on the dirty channel past 3. Haha. The Hxda looks amazing, but not ready to drop that much on an amp right now.